The invention relates to a constant velocity universal ball joint having an outer joint part with circumferentially distributed, substantially longitudinally extending inner ball tracks; an inner joint part with circumferentially distributed, substantially longitudinally extending outer ball tracks, the ball tracks in the outer joint part and inner joint part being arranged in pairs and positioned opposite one another while jointly accommodating a torque transmitting ball and participating or cooperating in controlling the balls towards and onto the plane which bisects the angle formed by the rotational axes of the outer joint part and inner joint part at articulation of the joint parts relative to one another, i.e. the angle-bisecting plane. The joint further has a cage which, in circumferentially distributed windows holds the balls in a common plane and guides them onto the angle-bisecting plane when the rotational axes of the outer joint part and inner joint part are articulated relative to one another.
The joints may be fixed joints which only permit the axes to be articulated but which do not allow the central planes of the outer and inner joint parts to be axially displaced relative to one another. However, the joints also include plunging joints where a relative displacement of the central planes of the outer and inner joint parts is possible.
Apart from directly controlling the balls so as to cause them to move onto the angle-bisecting plane by designing the tracks accordingly, as mentioned, it is in addition also possible to control the balls indirectly, by means of the cage, so as to cause them to move onto said plane. This assumes that the cage guiding faces at the outer joint part and at the inner joint part are designed in such a way--especially by axially offsetting their centers of sphere--that upon articulation of the axes of the outer and inner joint parts relative to one another, control forces are introduced directly into the cage. However, this type of control does not necessarily exist with the joints concerned here.
With fixed joints of the type as a rule and with plunging joints of the type as a matter of necessity, control of the balls by the tracks is effected in such a way that in the longitudinal direction, the tracks deviate slightly from the absolutely parallel design such that the tracks in the outer joint part and/or in the inner joint part, when projected onto the rotational axes, form opposed angles therewith, so that any two tracks facing one another and jointly accommodating a ball intersect one another. As a rule, the angles involved are opposed angles of identical size formed by cooperating tracks in the outer joint part and inner joint part. If with such a joint the rotational axes of the two joint parts are articulated relative to one another, the point of intersection of the tracks where approximately the ball is held, moves in the axial direction with reference to each of the two joint parts and thus guides the cage onto the angle-bisecting plane. Because the cage has been moved to the angle-bisecting plane and because, as a result, it is articulated relative to both the outer joint part and the inner joint part, it is due to simple geometric conditions that there takes place a relative circumferential movement of the balls relative to the cage during said movements. Therefore, the cage windows holding the balls in a common plane have to have a certain circumferential length. The greater the specific articulation angle of a joint, the greater the necessary circumferential length of the cage window.
As a result, the webs remaining between the windows are reduced in width, so that the fracture strength of the cage decreases.
With fixed joints of the type, the action of controlling the balls onto the angle-bisecting plane may also, when viewed in a longitudinal section, additionally be based on an angle of intersection of the track center lines of the tracks which are associated relative to one another and which jointly accommodate a ball. In this case, the track center lines, in the longitudinal section, are designed to be mirror-image symmetrical relative to the central plane and extend, for example, in the form of circular arches whose centers of curvature are axially offset in the direction opposite to said central plane. For the reasons already mentioned above, the cage windows also have to have a certain circumferential length which weakens the cage. Furthermore, there exists a problem in that an adequate track depth cannot be ensured in the axial end regions of such joints, so that when the joint is articulated and with the balls having moved into the axial end regions, the tracks are capable of accommodating limited circumferential forces only, which means that corresponding forces additionally have to be accommodated by the cage. As a result, the strength limit of the cage is again disadvantageously reduced.
It is the object of the present invention to improve a constant velocity universal ball joint of the initially mentioned type in such a way that the forces applied to the ball cage are reduced and that, as a result, the load bearing capacity of the cage under torque is increased when the joint is in an articulated condition.
The objective is achieved in that the ball tracks in the outer joint part and inner joint part are designed in such a way that, with coaxial axes and corresponding central planes of the outer and inner joint parts, in a radial projection onto the axes, they form with their center lines an angle relative to one another on both sides of the respective central planes, which deviates from zero and which decreases towards their axial ends.
With reference to fixed joints, the relative positions of the axes and central planes of the outer and inner joint parts mentioned above define the aligned joint in two ways, whereas with reference to plunging joints, they define the aligned joint in the central position of the possible plunging distance.
This means that with an articulated joint, the tracks especially in the articulation plane in the region of large angles no longer apply any control forces to the balls as soon as they have reached the nearly or completely parallel end portions, which means that the control forces are reduced and that, overall, the cage is subject to lower forces. In the tracks positioned outside the articulation plane, the track control angle subjecting the respective balls to control forces is always relatively large.
In the case of plunging joints, when in operation, a long plunging distance, as a rule, corresponds to a large articulation angle so that even with long plunging distances, the function of controlling the cage onto half the plunging distance is always ensured in spite of a decreasing control angle.
According to a first preferred embodiment which is easy to manufacture from a production or technical point of view, the central portions of the tracks of each of the two joint parts are inclined in the same direction, i.e. they extend essentially parallel relative to one another in each joint part, respectively.
According to a second preferred embodiment, the tracks of each of the two joint parts are arranged across the circumference so as to extend alternately at different angles of inclination. This improves the effectiveness of the control mechanisms.
As far as the track depth is concerned, the tracks may be designed in such a way that, like threads, they extend along their entire length at a constant distance from the respective rotational axis, with the end portions being axis-parallel. Alternately, it is also possible to design the tracks as inclined tangents at a circle positioned in the central plane of the joint, in which case the respective distance from the rotational axis is not constant, whereas the end portions are again parallel to the rotational axis.
In a radial projection, the tracks may be formed of straight portions. This may be advantageous from a production or technical point of view. However, it is also possible to provide for continuous changes in angle which lead to correspondingly continuous changes in the load conditions at the cage, thereby avoiding sudden load peaks. In this case, the invention permits several types of curves starting from the central plane, i.e. curves which, for example, follow hyperbolic, parabolic, elliptical or circular functions.